The present invention relates in general to fluidized bed systems, and in particular to a new and useful apparatus and method of transferring fluidized material between two separated fluid beds, for the purpose of substantially equalizing the level and quantity of bed material and pressure differential across the beds.
A fluid bed consists of a stream of air flowing upward through a dense bed of solid particles, at sufficient flow rate to suspend and mix the particles. At sufficiently high flow rate, bubbles of air are formed in the bed, causing a highly turbulent mixing of particles and air. The appearance is that of a boiling fluid and such a bed is referred to as a "bubbling bed".
At even higher gas flow rates, the particles become entrained in the air and combustion gas stream and are transported upwardly. The particles may be collected and then returned to the process. This is known as a "circulating fluidized bed".
The fluid bed is confined within an enclosure and is supported on an air distribution means such as a distributor plate in the enclosure. The air distributor may be perforated to admit air to the bed. Below the air distributor is a means of supplying fluidizing air such as an inlet plenum which is supplied with fluidizing air at a sufficient flow rate to fluidize the particles above the air distributor plate.
Fluid beds have been used for the combustion of coal and low grade fuels. An inert or reactive bed material, for example, sand or limestone, is suspended in a fluid bed. The material is then heated to the temperature required for the ignition of coal. Crushed and sized coal is then supplied into the bed for burning. The combustion temperature is generally held within the range of 1,500.degree. F. to 1,600.degree. F. While the reaction temperature can locally exceed 3,000.degree. F., a heat sink is provided in the bed for cooling the bed material to its operating temperature. This is done to keep the temperature below the softening temperature of ash (about 2,000.degree. F.) so as to avoid clogging and other problems during operation of the bed.
Fluidized bed combustors can be operated either at atmospheric pressure (atmospheric bed) or at elevated pressure (pressurized bed).
For pressurized operation, the fluid bed enclosure is normally positioned within a pressure vessel.
It is often useful to provide more than one fluid bed enclosure. This can increase the efficiency at which fuel is burned in the fluid bed. Problems may arise however in equalizing the level and quantity of bed material and pressure differential across the beds of separate enclosures.
U.S. Pat. No. 3,893,426 to Bryers discloses a divided fluid bed enclosure where part of the enclosure confines coarse grained fuel while the other part confines fine grained fuel. Openings are provided in the partition wall to allow communication between the two fluid beds.
U.S. Pat. No. 4,457,896 to Kono discloses a fluid bed enclosure having a plurality of vertically spaced beds where material from adjacent beds can be transferred by vertically extending tubes.
Neither of these references discloses structure which can establish communication between the fluid beds of entirely separate enclosures, while compensating for differences in expansion and contraction of the enclosures.